This invention relates generally to inflatable restraint systems and, more particularly, to the generation of inflation gas used in such systems. More specifically, the invention relates to inflation gas generation via a dissociating material and the moderation thereof.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, an airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as an "inflator."
"Rise rate", i.e., the rate at which the gas output from an inflator increases pressure, as measured when such gas output is directed into a closed volume, is a common performance parameter used in the design, selection and evaluation of inflator devices for particular vehicular airbag restraint system installations. It is commonly desired that an inflatable restraint airbag cushion initially inflate in a relatively gradual manner soon followed by the passage of inflation gas into the airbag cushion at a relatively greater or increased pressure rate. An inflator resulting in such inflation characteristics is commonly referred to in the field as producing inflation gas in accordance with an "S" curve.
Many types of inflator devices have been disclosed in the art for the inflating of one or more inflatable restraint system airbag cushions. Prior art inflator devices include both pyrotechnic inflators and compressed gas inflators. Unfortunately, each of these types of inflator devices has been subject to certain disadvantages.
For example, pyrotechnic inflators generally produce or derive inflation gas via the combustion of a gas generating material, i.e., a pyrotechnic. In practice, such gas generating materials can typically produce various undesirable combustion products, including various solid particulate materials. The removal of such solid particulate material, such as by the incorporation of various filtering devices within or about the inflator, undesirably increases inflator design and processing complexity and can increase the costs associated therewith. In addition, the temperature of the gases emitted from such inflator devices can typically vary between about 500.degree. F. (260.degree. C.) and 1200.degree. F. (649.degree. C.), dependent upon numerous interrelated factors including the desired level of inflator performance, as well as the type and amount of gas generant material used therein, for example. Consequently, airbag cushions used in conjunction with such inflator devices are commonly constructed of or coated with materials which are resistant to such high temperatures. For example, in order to resist being burned through as a result of exposure to such high temperatures, an airbag cushion such as constructed of nylon fabric can be coated with neoprene or the like temperature resistant material or include one or more neoprene coated nylon patches or the like placed at the locations of the airbag cushion at which the hot gas initially impinges. As will be appreciated, such specially fabricated or prepared airbag cushions typically are more costly to manufacture and produce.
The term "compressed gas inflator" is commonly used to refer to the various inflators which contain a selected quantity of compressed gas. For example, one particular type of compressed gas inflator, commonly referred to as a "stored gas inflator," simply contains a quantity of a stored compressed gas which is selectively released to inflate an associated airbag cushion.
A second type of compressed gas inflator, commonly referred to as a "hybrid inflator," typically supplies or provides inflation gas as a result of a combination of stored compressed gas with the combustion products resulting from the combustion of a gas generating material, e.g., a pyrotechnic.
In the past, stored gas inflators have been at a disadvantage, as compared to pyrotechnic inflators, in terms of size, weight and/or cost. This is especially significant in view of the general design direction toward relatively small, lightweight and economical modern vehicle components and assemblies. In particular, the need to store a gas within an inflator at relatively high pressures typically results in the need for thick-walled pressure vessels that tend to be more bulky, heavy and costly than otherwise desired.
Commonly assigned Smith et al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; Rink, U.S. Pat. No. 5,494,312, issued Feb. 27, 1996; and Rink et al., U.S. Pat. No. 5,531,473, issued Jul. 2, 1996 disclose and relate to a new type of inflator device, sometimes called a "fluid fueled inflator." Such inflator devices typically utilize a fuel material in the form of a fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or more combinations thereof, in the formation of an inflation gas for an airbag cushion. In one form of fluid fueled inflator, such a fluid fuel material is burned to produce gas which contacts a quantity of stored pressurized gas to produce inflation gas for use in inflating a respective inflatable device.
While such types of inflator devices can successfully overcome, at least in part, some of the problems associated with the prior types of inflator devices, there is a continuing need and demand for further improved apparatus and techniques for inflating an inflatable device such as an airbag.
In at least partial response thereto, further efforts have led to the development of apparatus for and methods of gas generation which at least in part rely on the decomposition or dissociation of a selected gas source material for gas generation. In particular, such developmental efforts have resulted in the development of an inflator device which is at least in part the subject of the above-identified patents: Rink, U.S. Pat. No. 5,669,629; Rink et al., U.S. Pat. No. 5,884,938; and Rink et al., U.S. Pat. No. 5,941,562. In one form of such newly developed inflator device, inflation gas is produced or formed, at least in part, via the decomposition or dissociation of a selected gas source material, such as in the form of a compressed gas and such as via the input of heat from an associated heat source supply or device. Nitrous oxide is a preferred gas source material disclosed in one or more of these patents. One or more of these patents disclose that such an apparatus for and method of gas generation can be helpful in one or more of the following respects: reduction or minimization of concerns regarding the handling of content materials; production of relatively low temperature, non-harmful inflation gases; reduction or minimization of size and space requirements and avoidance or minimization of the risks or dangers of the gas producing or forming materials undergoing degradation (thermal or otherwise) over time as the inflator awaits activation.
Nevertheless, there is a continuing need and demand for still further improved apparatus and techniques for inflating an inflatable device such as an airbag. In particular, there is an ongoing need and demand for such apparatus and methods which desirably favorably reduce one or more apparatus parameters such as weight, cost, complexity, and size, for example. Further, there is a continuing need and demand for such an improved apparatus and associated or corresponding inflation techniques or methods such as may either or both improve the safety and facilitate the ease of operation and manufacture.